Double-tuned intermediate-frequency transformer

ABSTRACT

A double-tuned intermediate-frequency transformer having a structure wherein two single-tuned intermediate-frequency transformers employing cap-type cores provided with center cores therein are arranged adjacent to each other being covered with one shielding case, and being adapted to a free choice of the degree of coupling between the respective coils of the two single-tuned intermediate-frequency transformers laid adjacent to each other through adoption of the cap-type cores each having a suitable sleeve length relative to the length of its center core.

United States Patent 1721 lnventor Kalutolno lwata Neyagawa-shi, Japan[21] AppltNo. 815,9l5 221 Filed Apr. 14, 1969 {45] Patented July 13,1971[73| Assignee Matsushita Electric Industrial Co., Lld.

Osaka, Japan [32] Priority Apr. 18, 1968 1 1 Jil [311 32631 [54]DOUBLE-TUNED INTERMEDIATE'FREQUENCY TRANSFORMER I China, 9 Drawing Figs.

[52] 1.1.8. Cl .1 336/83, 336/87, 336/131, 336/136 [51] lnt.Cl1101121106 [50] Field ofSmrch 336/33.84, B7, 131, 136

[56] Relerenoes Cited UNITED STATES PATENTS 1,634,923 7/1927 Thullen336/83 1,978,600 10/1934 Polydorofi 336/87 X 2,318,415 5/1943 Patzschkeet a1. 336/136 uuu Primary ExaminerThomas J. Kozma Attorney-Stevens,Davis, Miller & Mosher ABSTRACT: A double-tuned intermediate-frequencytransformer having a structure wherein two single-tunedintermediate-frequency transformers employing cap-type cores providedwith center cores therein are arranged adjacent to each other beingcovered with one shielding case, and being adapted to a free choice ofthe degree of coupling between the respective coils of the twosingle-tuned intermediate-frequency transformers laid adjacent to eachother through adoption of the cap-type cores each having a suitablesleeve length relative to the length of its center core.

PATENTED JUL13I9H 3.593245 SHEET 1 OF 2 FIG 30 /4 F/ 6 317 F/ G 30INVENI'OR Kalli-T0170 1 9"? ATTORNEYS Pmmm JUH mm 3.593; 245

SHEET 2 OF 2 INVENIOR lrnzumwro I warn BY duh 5 4444 7 ATTORNEYSDOUBLE-TUNED INTERMEDIATE-FREQUENCY TRANSFORMER The present inventionrSlates to double-tuned intermediatefrequency transformers beingemployed in transistor radios and television receivers.

A double-tuned intermediate-frequency transformer hitherto placed on themarket carrying a description noted for use in a transistor circuit isof a miniaturized type, and most of the double-tunedintermediate-frequency transformers have a structure wherein two singletuned intermediate-frequency transformers are arranged adjacent to eachother and the combination thereof is enclosed in one shielding case.However, there exists very little magnetic coupling between these coils,hence, either of the following two types of structures is generallyemployed, one type is an L-couplcd one wherein a portion of one coil Lis wound together with the other coil L, to obtain the coupling betweenthe two coils as is shown in FIG. 6a, while, the other is a C-coupledone wherein respective higher potential points of primary and secondarysides are connected with each other through a capacitor C as is shown inFIG. 6b.

In the above L-coupled type, there are involved those drawbacks thatcoils have complicated structures and much dispersion is to be seen inthe degree of coupling in the intermediatefrequency transformers for usein a higher frequency range such as in the case of FM due toirregularity in wiring of lead wires, etc., because the number of turnsof coil L to be wound for coupling in the above case is reduced to asfew as 0.5 to 1.5 turns.

Also, in the above C-coupled type because of a small capacity value of Csuch as L to 2.5 pF dispersion in the degree of coupling due to capacityvalue deviation has been inevitable.

The present invention is intended to eliminate the abovementionedexisting drawbacks.

According to the present invention, the magnetic coupling is adapted tobe obtained through the construction itself of a double-tunedintermediate-frequency transformer, and especially its degree ofcoupling can be easily varied by small changes in value.

According to the present invention, either a core supporter or a centerhole of a terminal plate is provided with a thread so that both membersmay be threadedly engaged with each other, and manufacturing efficiencycan be remarkably increased as compared with a manufacturing method bywhich a core itselfis to be threaded.

In adjusting the double-tuned intermediate-frequency transformeraccording to the present invention, a cap type core is rotated under anexternal force. Even if a distortion force may be applied to a centercore of the cap type core in this case such a distortion force may beabsorbed by the core supporter thereby preventing the center core frombeing damaged.

A detailed description will, hereunder, be given of an embodimentaccording to the present invention referring to the accompanyingdrawings, wherein:

FIG. I is a sectional view of an embodiment of the doubletunedintermediate-frequency transformer according to the present invention;

FIG. 2 is a perspective disassembly drawing showing the construction ofa single-tuned intermediate-frequency transformer comprised in the abovedouble-tuned transformer;

FIGS. 3a to 3c are sectional views each showing respective examples ofthe cap type cores provided with center cores therein to be employed inthe above double-tuned transformer;

FIG. 4 is an electric circuit diagram of the above doubletunedtransformer;

FIG. 5 shows performance characteristics each according to therespective combinations of the cap type cores shown in FIGS. 30 to 3cbeing employed in the above double-tuned transformer; and

FIGS. 6a and 6b .are electric circuit diagrams of conventionaldoubleduned intermediate-frequency transformers.

Referring to FIGS. 1 and 2, l designates a terminal plate provided witha tapped hole 2 at its center and a winding portion 4 for a coil 3 atits upper portion. The tapped hole 2 in the terminal plate I isperforated therethrough, and a shank por tion 6 of a core supporter 5made of thermoplastic resin or the like is engaged therein through aself-tapping method. That is to say, a plurality of ridges 7 to bethreaded thereon are provided axially on the peripheral surface of theshank portion 6, which ridges 7 are put into the tapped hole 2 of theterminal plate I being turned round and threaded by themselves, thusbeing self-tapped, if expressed by the word used above. Further, aflange 8 at the upper end of the shank portion 6 of the core supporter 5is provided with two protrusions 9, from which flange 8 down to theshank portion 6 thercthrough formed is a hole portion 10.

The core supporter 5 having such a construction is united with a captype core 12 having a pot shape and a center core ll at its centerportion.

To say more precisely, two perforations 13 are provided in the top wallof the cap type core [2, each of the perforations being placed at therespective positions opposite to the protrusions 9 on the above coresupporter 5, and the above protrusions 9 are inserted into theperforations 13 respectively, then, the protrusion tips are welded byfusion thereby uniting the core supporter 5 and the cap type core 12with each other. Further, the center core II in the above cap type core[2 is fitted into the hole portion 10 in the core supporter 5, and anadjusting slot 14 is formed on the top surface of the cap type core 12.Terminal pins l5 are embedded in the above terminal plate 1, and theterminal plate 1 is also provided with outlet slots 16 for lead wires.

A double-tuned intermediate-frequency transformer such as shown in FIG.1 can be obtained by arranging two singletuned intermediate-frequencytransformers each having a structure such as described above adjacent toeach other and covering them with one shielding case I7.

Further, 18 in FIG. 1 designates tuning capacitors which are disposedwithin hollow portions 19 provided in the bottom surface of the terminalplate 1. Numeral 20 designates adjusting window portions provided in theupper wall of the shielding case I7.

The electric circuit of the double-tuned intermediatefrequencytransformer having such a structure is shown in FIG. 4.

In FIG. 3, sections of the cap type cores l2 to be employed here areshown.

In such a case that two single-tuned intermediate-frequency transformersare arranged adjacent to each other as shown in FIG. 1 and as describedabove, magnetic flux flows mainly through the center core ll and asleeve portion 12' of the cylindrical body of each of the cap type core12, however, a part of the magnetic flux interlinks with the adjacentcap type core 12. Thus, magnetic coupling is produced as a result ofsuch mutual magnetic flux interlinkage between two singletunedintermediate-frequency transformers.

Now, in case that the cap type core 12 shown in FIG. 3a is employed ineach of the primary and secondary coils, the magnetic flux induced byone of the coils is magnetically shielded to a considerable extent bythe comparatively long sleeve 12', therefore, the magnetic leakage fluxwhich goes out of the cap type core is comparatively small. On thecontrary, if the cap type core 12 shown in FIG. 3c is employed as in theabove case, the magnetic flux induced by one of the coils passes fromthe tip of the center core II to the lower end of the sleeve 11',however, the magnetic flux path is more open compared with that in thecase of H0. 30, hence, the magnetic leakage flux is considerably large.

Thus, mutual coupling is obtained through the leakage magnetic fluxgoing out of the two cap type cores 12, therefore, the degree ofcoupling between the primary and secondary coils varies depending on therespective quantities of both magnetic leakage flux. This phenomenon isbeing utilized in the intermediate-frequency transformer according tothe present invention. Then, if an operating Q value is given for eachcoil, the pass band width as of the double-tuned intermediate-frequencytransformer can be freely determined by changing the length of thesleeve portion 12' of the above cap type core [2, corresponding to thepass band width to be desired.

ln case that the cap type cores l2 shown in FIGS. 30 to 30 are employedcombining each two cap type cores of the same type in pairs, in regardto the pass band width as of the doubletuned intermediate-frequencytransformer, that of the FIG. 3b type is wider than that of the FIG. 30type and that of the FIG. 3c type is still wider than that of the FIG.3b type. The above response characteristics are shown in FIG. 5 beingcompared with each other.

The double-tuned intermediate-frequency transformer ac cording to thepresent invention being so constructed as described above, the degree ofmagnetic coupling between primary and secondary coils thereof can bechosen freely in practical use through adoption of any cap type coreschosen freely from those having various shapes. Moreover the structureof each coil in an embodiment according to the present invention can bemade simple and easy to manufacture. Furthermore, the present inventioncan have other individual components such as required in a conventionalC-coupled type, thus bringing about another advantage in cost reduction.

In addition, because the coupling between the primary and secondarycoils therein is obtained magnetically and not capacitively, therebybringing about a sharp skirt form in a response characteristic curve fora given pass band width, the selectivity characteristic is made betterthan in any conventional types.

Thus, the double-tuned intermediate-frequency transformer according tothe present invention may be said to have great value in practical useas described above.

What I claim is:

l. A double-tuned intermediate-frequency transformer comprising aplurality of single-tuned intennediate-frequency transformers disposedadjacent to each other, each of said single-tuned intermediate-frequencytransformers comprising, in combination: a winding portion having acenter hole therein disposed at the center of the upper surface of aterminal plate, a coil wound on the outer periphery of said windingportion, a core supporter having a cap type core provided with a centercore securely fixed to the upper portion thereof threadedly fitted intosaid center hole; a single shielding case covering said plurality ofsingle-tuned intermediate-frequency transformers; wherein the degree ofmagnetic coupling via the air gap between the respective coils of saidplurality of single-tuned intennediate-frequency transformers is freelyadjustable by the suitable selection of the length of a sleeve portionof said cap type core relative to the length of said center core,respectively, thereof.

1. A double-tuned intermediate-frequency transformer comprising aplurality of single-tuned intermediate-frequency transformers disposedadjacent to each other, each of said single-tuned intermediate-frequencytransformers comprising, in combination: a winding portion having acenter hole therein disposed at the center of the upper surface of aterminal plate, a coil wound on the outer periphery of said windingportion, a core supporter having a cap type core provided with a centercore securely fixed tO the upper portion thereof threadedly fitted intosaid center hole; a single shielding case covering said plurality ofsingletuned intermediate-frequency transformers; wherein the degree ofmagnetic coupling via the air gap between the respective coils of saidplurality of single-tuned intermediate-frequency transformers is freelyadjustable by the suitable selection of the length of a sleeve portionof said cap type core relative to the length of said center core,respectively, thereof.